Hydraulic tensioners for traction element drives, such as chain or belt drives, of internal combustion engines are known, for example from U.S. 2008/0015069. Because the length of the traction element changes due to heat and wear, its pre-tensioning must be readjusted continuously, and hydraulic tensioners have been proven to be the most reliable for this purpose. The hydraulic tensioners not only remove slack from the tension element, but can also compensate for vibration in order to maintain a firm contact between the guide element which is acted on by the tensioner and the traction element.
In many cases due to the high dynamics of the chain drive systems, high and fast tensioner displacements occur which result in abnormal peak pressures inside the high pressure chamber of the hydraulic tensioner. These peak pressures are highly undesirable as they create high loads on the traction element which can result in early failure of the traction element or one or more of the traction element guides. In order to avoid this, pressure relief valves have been incorporated into hydraulic tensioners, for example within the piston head of the tensioning piston as shown in U.S. 2008/0015069, or within the space inside the piston, for example as shown in EP 1 101 975. Other known tensioners are shown in EP 0 952 375, EP 0 067 314, DE 103 27 024, EP 1 258 655 and EP 1 201 964.
These known devices suffer from relatively complex and costly construction while not providing an effective means to not only vent or de-aerate any air trapped within the high pressure chamber, which can lead to a soft or spongy tensioning force, but also to provide a reduced volume for the high pressure chamber, which allows the tensioner to reach its full working characteristic as quickly as possible upon engine start up.